I have a couple of articles here that can help you troubleshoot this issue:
You may also need to see the recommended setting for iOS and OS X device use to properly configure the router for these connections:
Thanks for coming to the Apple Support Communities!
You're not alone JooCoelho
Friends of mine have the same weird problem. An iMac, not very old, it can't connect with their router, don't remember the brand. So They connect by ethernet. When their router was "game over" they borrow my Airport Express (first gen) and urprise ! wifi is working
But last week they bought a TP-Link, because I need my Apple one back, when troubleshooting in my community. Guess what... The iMac is no more working on wifi... OK, before to call this mac "brandist" (name for a racist router you see ) I'll see the Braden's suggestion.
With years, I' ve learned a couple of things ; never have an argument with a machine... So my friends will buy an Apple router (BTW they are excellent stuff) and things will be fine. But I want to understand, so...